1. Field of the Invention
The present invention relates to a communication system using a light guide, and particularly, relates to a sheet light guide which is formed in a manner that the sheet light guide contains light-scattering particles in a sheet optical medium, and propagates light incident from one end surface thereof to the other end surface side while scattering the light by the particles.
2. Description of the Related Art
Heretofore, for example, as described in U.S. Pat. Nos. 5,548,670 and 5,542,017, a light guide is known, which is formed by containing light-scattering particles in an optical medium such as polymethylmethacrylate (PMMA), and propagates light incident from one end surface thereof to the other end surface side while scattering the light by the particles.
Such a light guide is that which propagates the light while repeatedly scattering the light by the particles in the optical medium in addition to the action of total reflection at an interface between a side end surface of the light guide and a surrounding medium (air or cladding layer). Accordingly, in comparison with a light guide which propagates the light only by the action of the total reflection, the light guide thus described has an advantage in that light, the intensity thereof being made more uniform, can be taken out of an emitting end surface. For example, as described in U.S. Pat. No. 5,822,475, it is conceived, by utilizing this advantage, to apply such a type of light guide to the purpose of constituting an optical data bus (sheet bus). The optical data bus is that which is formed by use of a sheet optical medium, and in which one input unit inputting an optical signal is coupled to one end surface thereof, and a plurality of output units are coupled to the other end surface, thus distributing the inputted optical signal as a common signal to the plurality of output units.
Moreover, for example, as described in Japanese Unexamined Patent Publication No. 11 (1999)-31035, as such an optical data bus, one is also known, in which light-scattering portions are provided on a light-incident-side end portion of the sheet optical medium so as to correspond to respective signal light incident portions, and signal light scattered and branched by the light-scattering portions is propagated toward a light-emitting-side end portion of the optical medium.
A communication system using a sheet light guide formed by containing the light-scattering particles in the sheet optical medium as described in U.S. Pat. No. 5,822,475 can also be introduced into various instruments. In such a case of introduction, a sheet light guide must often be bent. However, in general, the sheet light guide has some thickness and is not very flexible. Accordingly, when a space in such an instrument is narrow and has a complicated shape, sometimes it becomes impossible to place the sheet light guide therein in a bent manner. This point becomes a serious problem in terms of replacing a communication system using electric wires in the instrument with the communication system using the sheet light guide.